Correlation between enhanced oxygen evolution and β→γ phase transition in Mn-doped NiOOH

NiOOH is a promising electrocatalyst for the oxygen evolution reaction (OER). Here we systematically investigate the effect of Mn doping on the structure, oxidation state, bond length, phase transition, and OER activity of NiOOH using dispersion-corrected hybrid density functional theory (HSE06+D3) combined with experimental material characterization and electrochemical measurements for samples that were prepared through a synthesis route mimicking Ni recovery from wastewater with circular-material benefits. Our results reveal that Mn doping promotes not only the formation of surface oxygen vacancies but also the phase transition from β- to γ-NiOOH, a critical step overlooked by previous studies. This Mn-doping is found to largely reduce the calculated overpotential, especially with respect to undoped β system, in very good agreement with experimental observations.